Despite dramatic improvements in human health, the average birth-weight of babies has not increased over the last 150 years, say researchers. The study conducted by a team at the London School of Economics and Political Science (LSE) found that average birth weights, as well as the share of babies born at different birth weights, are very similar today as they were in the nineteenth century in Europe and North America. In contrast, average adult height and life expectancy has increased dramatically.

Dr. Eric Schneider, Assistant Professor of Economic History at LSE and author of the paper, said: Birth weights are used by health care professionals as a proxy for the health of babies in the womb. Understanding health conditions in the womb is also significant as they have been shown to affect children’s health across their entire life, even into old age.

These findings question international birth weight standards that determine the 'ideal' weight that a baby should be, as developed by a the International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st), a global network of more than 300 researchers and clinicians from 27 institutions in 18 countries worldwide and coordinated from the University of Oxford.

For instance, in Pakistan, 32 percent of babies are born at a low birth weight, meaning that they weigh in at less than 2500 grams, and it is assumed that if maternal health conditions improve, average birth weights will rise. However, given that this did not happen in Western Europe and the United States, despite significant historical improvements to maternal health care, it is possible that birth weights in Pakistan will not increase to the level set by the INTERGROWTH-21st standards.

The researcher team emphasizes that their results do not in any way downplay the very real health risks low birth weight babies face or the fact that children developing in the womb are extremely sensitive to poor conditions, such as a lack of key nutrients or infection. The study only looks at statistics at a population level to analyze what they reveal on the general rather than the individual level.